<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div,p,h3{
            color:orange;
        }
        p,h3,figure,ul,ol{
            margin:0;
            padding:0;
        }

        div p{
            color:red;
        }
        div p span{
            color:green;
        }
    </style>
</head>
<body>
    <div>今天</div>
    <p>明天</p>
    <h3>后天</h3>

    <div>
        <p>我是一个子类元素
            <span>
                我是一个孙类元素
            </span>
        </p>
    </div>
</body>
</html>